1. Field of the Invention
The invention concerns surfactant combinations as the basis for water-based shampoos, bath and shower gels as well as other cosmetic formulations, i.e. liquid cleaners or other systems for which an increased viscosity is necessary for application reasons.
2. Discussion of the Background
In the past, liquid cleaner systems were based predominantly on alkyl sulfates or alkyl ester sulfates, generally with a low degree of ethoxylation. In these cases, viscosity can be adjusted relatively easily by adding sodium chloride, ammonium chloride, optionally also combined with fatty acid diethanolamides and/or other additives. Although such formulations demonstrate satisfactory foaming and are inexpensive, they do, however, have the disadvantage of being very irritating to the skin as well as to the mucous membranes of the eyes, which is of significant importance in view of increasingly frequent, in some cases daily use. Because of the risk potential of trace contaminants of N-nitrosodiethanolamine, it is also desirable to have available formulations which are as free of nitrogen as possible (see Hamke Meijer, Seifen-Ole-Fette-Wachse 114, 159 (1988)).
Milder surfactant preparations which do not have the disadvantages listed above but can also be thickened easily are therefore desirable. Inexpensive surfactants which are gentle to the skin and mucous membranes cannot be sufficiently thickened with electrolytes (H. Meijer, Seifen-Ole-Fette-Wachse 113, 135 (1987) and H. Tesmann, Parfumerie und Kosemetik 68, 630 (1987)). Attempts have therefore been made to achieve sufficiently high viscosity or thickening by increasing the surfactant concentration or by means of limited partial substitution of the ether sulfate with a milder and toxicologically unproblematical surfactant (H. Meijer, loc. cit. and U.S. Pat. No. 3,038,862). This does not, however, deal with the disadvantages listed above in a satisfactory manner. Thickening by means of water-soluble polymers is not considered a suitable alternative, due to the influence on the foam quality.
Carboxymethylated oxyethylates are considered to be mild surfactants which are gentle to the skin and mucous membranes, and are described as very good in this regard (N.A.I., Seifen-Ole-Fette-Wachse 109, 353 (1983)). These oxyethylates have the decisive disadvantage that they cannot be thickened with usual electrolyte concentrations, or can only be thickened insufficiently (EP-A 0 176 151).
Alkyl oligoglycosides also demonstrate very good properties with regard to tolerance for the mucous membranes (A. D. Urfer et al., Poster presentation, Second World Conference on Detergents, Montreux, 1986). But the alkyl oligoglycosides, especially those with a degree of glycosidation of 1 to 1.45, prove to be completely unsatisfactory with regard to thickening with electrolytes. Such alkyl oligoglycosides are usually insoluble in water at concentrations below 10% by weight, or at least have low solubility, which results in very cloudy or even two-phase dispersions in the presence of electrolyte.
A need continues to exist, therefore, for surfactant combinations which can be thickened with electrolyte, which are gentle to the skin and mucous membranes, and which are extensively free of ether sulfates and surfactants containing nitrogen.
The use of combinations of alkyl polyglycosides or alkyl oligoglycosides with anionic surfactants has been known for a long time.
DRP 593,422, for example, describes the use of cetyl maltoside with common soap, U.S. Pat. No. 3,721,633 concerns the use of mixtures of alkyl polyglycosides with anionic synthetic surfactants, such as dodecyl benzenesulfonate, for example, and the Technical Bulletin Triton CG 100 of Rohm and Haas dated 1975 mentions a mixture of alkyl polyglycoside with lauryl ether sulfate, among other things.
WO 86/02943 describes the combination of alkyl monoglycosides and/or alkyl oligoglycosides with various anionic surfactants such as alkyl sulfates, alkyl ether sulfates, olefin sulfonates, paraffin sulfonates or alkyl benzene sulfonates, with the goal of increasing viscosity. Contrary to the present invention, the anionic surfactants claimed are not very gentle to the skin and mucous membranes, which is of significant importance.
The combination of alkyl polyglycosides with alkyl benzenesulfonate and with carboxymethylated alkanoloxyethylates, among other things, is mentioned in EP 0 070 075, where a clearly higher degree of glycosidation of the glycosides is present.
Thickening with electrolytes, which is demonstrated by the combinations of alkyl oligoglycosides and carboxymethylated alkenoloxyethylates according to the invention, is not present. The combinations of alkyl oligoglycosides with carboxymethylated alkyl phenoloxyethylates also cannot be thickened with electrolyte.